Trinuclear methine dyes for use in electrophotographic system

ABSTRACT

Trinuclear methine dyes and intermediates therefor, prepared by quaternizing oxonols, converting the quaternary compound to an inner anhydride, and condensing the latter with a heterocyclic compound having a reactive methyl or methylene group to yield a trinuclear methine dye; and use of the resulting dye to sensitize photoconductive zinc oxide for electrophotography.

United States Patent 2,535,994 12/1950 Thompson 96/105 X 2,535,995 12/1950 Thompson.. 96/105 3,047,384 7/1962 Jones et a1. 96/1.7 3,476,558 1 1/1969 Depoorter et a1 96/1.7 3,507,649 4/1970 Hensley 96/1 .7

Primary Examiner-George F. Lesmes Assistant Examiner-R. E. Martin AttorneysGeorge L. Tone, Walter C. Kehm and Samson B.

Leavitt ABSTRACT: Trinuclear methine dyes and intermediates therefor, prepared by quaternizing oxonols, converting the quaternary compound to an inner anhydride, and condensing the latter with a heterocyclic compound having a reactive methyl or methylene group to yield a trinuclear methine dye; and use of the resulting dye to sensitize photoconductive zinc oxide for electrophotography.

TRINUCLEAR METHTNE DYES FOR USE IN ELECTROPHOTOGRAPHIC SYSTEM This invention relates to novel trinuclear methine dyes, intermediates therefor, a process for their preparation, and their use in sensitizing zinc oxide as a photoconductor in electrophotographic materials.

It was known heretofore that reactive derivatives of 3-alkylrhodanines, substituted in 5-position, by acetanilinomethylene-, anilinomethylene or ethoxymethylenradicals (US. Pat. Nos. 2,494,031, 2,658,890) could be used as starting materials for preparation of complex salts of bisrhodanine-methine or oxonol dyes. Moreover, bis-rhodaninemethine dyes have been prepared from 3-alkylrhodanines by reaction with ethylorthoformate or diethoxymethylacetate (U.S. Pat. No. 2,533,206) in a basic condensation rriedium. Thus, preparation of oxonol or bis-rhodanine-methine dyes is well known in the art. I

It is an object of this invention to provide a novel method for preparing quaternary anhydro inner salts from oxonols and to prepare novel trinuclear dyes from the resulting inner salts, as well as to incorporate said dyestuffs as sensitizers for photoconductive zinc oxide in electrophotographic coatings.

In accordance with this invention, an oxonol dye is converted to a quaternary salt, and the latter hydrolyzed to an anhydro inner salt by purification in a polar solvent. The resulting quaternary anhydro inner salt is then condensed with a N- heterocyclic compound having a reactive methyl or methylene group to form a novel class of trinuclear methine dyes. The latter are incorporated as sensitizers in photoconductive zinc oxide coatings for use in electrophotographic materials.

More particularly, in accordance with this invention, an oxonol corresponding to one of the following formulas:

wherein R and R, are lower saturated or unsaturated alkyl or carboxy alkyl groups or phenyl groups, R is a lower alkyl group, A is a phenyl group and Y and Z represent a nonmetallic atom (such as N, O, S, Se) necessary to complete a heterocyclic nucleus containing five atoms in the heterocyclic ring, as for example, a rhodanine nucleus, a thiazole-2,4-dione nucleus, a 2-thiooxazolidone nucleus or the like, is treated with a quatemizing reagent such as dimethyl sulfate or methyl or ethyl paratoluene sulfonate. The resulting quaternized complex salt is purified by heating in a polar solvent-especially a lower alcohol such as methyl, ethyl or isopropyl alcohol, preferably diluted to about 50 percent concentration with water. The quaternary compound is hydrolyzed by this treatment to a quaternary anhydro inner salt which separates from the solvent-the salts resulting from the compounds corresponding to the formulas above indicated having the following formulas respectively:

and

wherein R represents a lower alkyl or lower carboxyalkyl group, and X represents the nonmetallic atoms necessary to complete a heterocyclic nucleus having five to six carbon atoms in the heterocyclic ring. The resulting trinuclear dyes correspond to the general formulas:

wherein R, R,, R R,, A, X, Y and 2 have the same significance as indicated hereinabove.

My invention will be illustrated by the following examples wherein parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 6.5 grams of the complex inner salt of bis-l 5-(3-ethylrhodanine)-methine cyanine lwere preheated with 30 ml. of purifled chlorob enzene on a constant temperature bath at l3l C. for l minutes. 30 ml. of purified dirnethyl sulfate were added. and heating continued for 5 minutes at the same temperature. Upon cooling, the mixture was treated three times with ethyl ether. The oily residue was then boiled with l8 ml. isopropanol and then diluted with 18 ml. of water. Upon cooling, the quaternary inner anhydro salt separated in the form of a reddish-brown solid having a melting point of 236-237 C. Upon analysis, it was found to correspond to the empirical formula C, H,.,N-,O S;,-the yield being 4.61 g. corresponding to 93.1 percent of theory. lts formula is as follows:

EXAMPLE 2 18.54 g. of the aforesaid anhydro inner salt of example l were added. together with 20.2 g. of learboxyethyl-(vmethoxy-Z-methyl-benzothiazolium iodide, to lSO ml. of isopropanol. After mixing thoroughly, 34.28 ml. of triethylaminc were added. After stirring for 2 minutes, the mixture was heated to boiling for 3 minutes, and then diluted with three times its volume of water. After neutralizing with 37.7 ml. of glacial acetic acid. the mixture was cooled in ice water for 20 minutes. The dyestuff which separated from the solution was recovered by filtration and boiled three times with methanol. 18.02 g. (59.7 percent of theory) of dyestuff was obtained in the form of greenish crystals melting at 24024 1 C. with decomposition. On analysis, it was found to correspond to the empirical formula c H N O s -cH OH. llts formula is as follows: I

| ciincooii A series of examples were carried out utilizing the procedure of example I, but substituting for the oxonol inter mediate, a molecularly equivalent amount of an oxonol intermediate corresponding to the formula:

| I It R which yielded a series of anhydro inner salts corresponding to the formula:

Y-(J ClIC-? U- r S t ll:

l l o e 0 0 o *(7 l l R R wherein Y, R and R, corresponded to the moieties indicated in the following table:

TABLE 1 Example No Y R R l S methyl ethyl 4 S allyl ethyl i S allyl allyl 6 S carhoxycthyl ethyl 7 S allyl methyl R S phenyl ethyl q 0 ethyl In addition. the same procedure was employed to convert the oxonol intermediates shown in examples l0 and l l to their quaternary anhydro inner salts, the reactions being represented as follows;

EXAMPLEIO (1H, t (ll (-s o 0 h N N (5H5 ll ll; ":Cll S ll N C ()"C SCH;

\ l T Co s ll EXAMPLEll s -tlxzo S t C: Cll I 0 --c ces (l ll;

O 'C C :CH (HZ? N 0C C SCH;

| (lzl i N (gllg wherein Y, M, R, R and R signify the moieties shown in the following table:

carboxyethyl Additional trinuclear dyestuffswere similarly prepared in a further series of examples from intermediate quaternary anhydro salts by condensation in the manner above illustrated, ths eaction being formulated as follqws:

wherein Y, R, R and R have the significance indicated in the following table:

The intermediate quaternary anhydro inner salt of example .10 was condensed with 2-methyl--methoxy-3-carboxyethylbenzothiazolium iodide in accordance with the procedure of example 2 to form a trinuclear methine dye having the following formula:

EXAMPLE 30 The intermediate anhydro salt of example 11 was condensed with 2-methy l-6-methoxy-3-carboxyethylbenzothiazolium iodide in accordance with the procedure of example 2 to form a trinuclear methine dye having the formula:

The trinuclear dyestuffs as prepared in accordance with examples 12 to 30, are excellent sensitizers for zinc oxide in 15 photoconductive insulating layers in electrophotographic materials. In preparing such materials, photoconductive zinc oxide is mixed with a solution in a volatile organic solvent of a resin adapted to serve as an insulating binder, and a solution of the trinuclear sensitizing dye in a compatible solvent such as methanol or ethanol is added. After thorough mixing, the mixture is coated on a paper base, preferably impregnated with a salt such as an alkali or alkaline earth metal halide, or a cationic resin, e.g., of the type described in US. Pat. No. 3,01 1,918, to increase its electrical conductivity. The following example illustrates preparation of an electrophotographic material in accordance with this procedure:

EXAMPLE 31 0.09 g. each of 6 percent by weight xylene solutions of cobalt naphthenate and manganese naphthenate were dissolved in 260 ml. of toluene. 91.8 g. of 50 percent by weight solution in xylene of a resin consisting of a polyglycidyl ether of bis-para-hydroxyphenyl-dimethylmethane, esterified with soyabeanfatty acids and dimerized linseed fatty acids, and 18.2 g. of 67 percent by weight solution in xylene low molecular weight polystyrene (mp 75 C.) were added to the solution. Four hundred and fifty-four grams of photoconductive zinc oxide (St. Joe PC-331) were then added, and the mixture milled until smooth. Twenty milligrams of the dye of example 2, dissolved in 20 ml. of methanol were added, and the mixture thoroughly agitated for minutes. It was then coated on a paper base containing as a conductive increasing component, polyvinyl-benzylamine hydrochloride, and dried. The coating amounted to 20 lbs. of solids per 3,000 sq. ft. of surface. As compared with papers prepared instead with eyanine dye sensitizers having the following formulas:

the products prepared with trinuclear dyes of the present invention, possessed about 15-20 percent greater sensitivity.

The trinuclear dyestuffs of the present invention were also much more readily soluble in organic solvents than the foregoing cyanine dyes and were about 50 percent better than said cyanine dyes in resistance to bleaching on exposure to light when incorporated in electrophotographic zinc oxide coatings.

For purposes of sensitizing zinc oxide as a photoconductor for electrophotography, the trinuclear dyes of this invention having at least one carboxyalkyl group joined to a heterocyclic nitrogen atom are preferable.

Variations which will be obvious to those skilled in the art can be made in the foregoing examples without departing from the scope or spirit of the invention.

1 claim:

1. An electrophotographic recording element having, on a relatively conductive base, a coating comprising photocon ductive zinc oxide sensitized with trinuclear methine dye and provided with an insulating resinous binder for said sensitized zinc oxide, said trinuclear methine dye being selected from the class having the formulas:

wherein R and R are selected from the class consisting of saturated and unsaturated lower alkyl and carboxyalkyl groups, and phenyl groups, R is a lower alkyl group, A is a phenyl group, Y and Z are selected from the group consisting of N, O, S, Se atoms necessary to complete a heterocyclic: nucleus containing five atoms in the heterocyclic ring and Q represents a radical selected from the class consisting of those having the formulas;

wherein P represents an anion, X is selected from the class consisting of N, O, S, Se and C atoms necessary to complete a heterocyclic nucleus containing from five to six atoms in the heterocyclic ring and R is selected from the class consisting of 5 lower alkyl and carboxyalkyl groups, at least one of the substitutents at R, R and R being a lower carboxyalkyl group 2. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula;

(l lhCUUll 3. An electrophotographic recording element as delfined in 20 claim 1, wherein said trinuclear methine dye has the formula:

4. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula:

5. An electrophotographic recording element as defined in 45 claim 1, wherein said trinuclear methine dye has the formula: 

2. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula:
 3. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula:
 4. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula:
 5. An electrophotographic recording element as defined in claim 1, wherein said trinuclear methine dye has the formula: 